A SEMINAR REPORT ON

WIRELESS ELECTRICITY (WiTricity)

Submitted for the requirement of award of Bachelor’s Degree in Electrical Engineering

Submitted by:-

Mr. PRIYABRATA SAHOO Electrical Engineering Roll No.-26231

Regn No.-0701105103 7TH SEMESTER,B.TECH

Under the guidance of :

Prof. Pravat Ku. RayProfessor, Department of Electrical Engineering,

INDIRA GANDHI INSTITUTE OF TECHNOLOGY, SARANGDHENKANAL,ODISHA-759146

CERTIFICATE

This is to certify that Mr. Priyabrata Sahoo of 4th year,7th

semester, Bachelor in Technology ,Electrical Engineering, Roll No.-26231,Registration No.-

0701105103 has completed the seminar entitled “WIRELESS ELECTRICITY or WiTricity” for partial fulfilment of requirement of B.Tech 4th year 7th semester of BPUT examination, Odisha for the academic year 2010-2011.

Name of the guide- Prof. Pravat Ku.Ray

Signature of guide:

Date:

Signature:

Head of the Department

Prof. (Dr.) Bibhu Prasad Panigrahi

Date-

ACKNOWLEDGEMENT

I express my sincere gratitude to my concerned teacher and guide Prof. Pravat Ku. Ray, Professor, Department of Electrical Engineering, for his valuable and inspiring guidance towards the progress on the topic “WIRELESS ELECTRICITY or WiTricity” and providing valuable information for the development of my report.

Last but not the least I express my sincere and hearty thanks to all those who have directly or indirectly helped me in completing this seminar presentation and report successfully.

Date:

Place-IGIT,SARANG Priyabrata Sahoo

CONTENTS1.INTRODUCTION

2. WHY DO WE GO FOR WIRELESS POWER TRANSMISSION (WPT) SYSTEM 2.1-Losses in the wired system 2.2-Some advantages of WPT

3. HISTORY OF WPT

4. THEORIES ON WPT

4.1-Near field theory

4.1.1-Electrical conduction principle

4.1.2-Electrostatic induction principle

4.1.3-Electro-dynamic induction (resonant inductive coupling method/Evanescent coupling method )

4.1.4-Experimental demonstration of evanescent coupling at MIT4.2- Far field theory 4.2.1 – Microwave Power Transmission (MPT) 4.2.2-Applications 4.2.3- Safety issues5. How WPT technology works

6. OVERVIEW OF FUTURE WITH WIRELESS TRANSMISSION OF ELECTRICITY

7. CONCLUSION1. INTRODUCTION Today we do live in the “wireless age”, in which the air that we breathe probably contains more information than oxygen. However, this is also an age where mobile phones, MP3 players, laptop computers and domestic robots exist alongside old-fashioned power

wires and bulky batteries. Unlike information, electrical energy is still physically confined to these borderline anachronistic appliances. Overcoming these last obstacles would finally make this a truly wireless world. It all started a few years ago when Marin Soljac`´ic´, a physicist at the Massachusetts Institute of Technology(MIT) in the US, was driving back home one cold winter night and he heard an unfriendly beep from his mobile phone. It was the annoying reminder that the battery was running out, once again. It then suddenly occurred to Soljac`´ic´how great it would be if the mobile phone could take care of its own charging. The next morning, he returned to his office at the MIT determined to find a solution to the problem. An exhaustive literature search soon revealed that wireless transmission of power was not an original idea. Back in the 1890s Nikola Tesla, one of great pioneers of electromagnetism, was the first to envisage that electricity, then a newly found form of energy, should be delivered to every house, in every city, in every country on the planet. However, Tesla did not foresee that people would be willing to drag wires around the entire globe to use electricity. Instead, he dreamed of a way of transferring electrical energy wirelessly over long distances. This would be achieved using big, coupled electromagnetic resonators able to generate very large electric fields, which were meant to propagate most likely either via conduction through the ionosphere (presumably including gigantic sparks) or through the Earth (possibly via intermediate coupling to the Earth’s charge resonances, so-called Schumann resonances). The epitome of Tesla’s efforts to achieve his goal was Wardenclyffe Tower, a 57 m high structure in Long Island that was meant to deliver electricity to the entire planet. The construction was interrupted in about 1905, not because the method was considered impractical or dangerous, but because the funder, the famed financier and banker J P Morgan, was concerned that there would be no way to bill remote electricity users. Nowadays, more than a century after Tesla, electricity reaches nearly every home through a global electrical grid. Nevertheless, J P Morgan’s objections meant a premature end to the first attempt at wireless electricity. In the near future, wireless electricity could replace the ubiquitous power cable.2. WHY DO WE GO FOR WIRELESS POWER TRANSMISSION (WPT)SYSTEM?2.1-LOSSES IN THE WIRED SYSTEMProfessor Rauscher showed that the earth’s magnetosphere contains sufficient potential energy (at least 3 billion kilowatts) so that the resonant excitation of the earth-ionosphere cavity can reasonably be expected to increase the amplitude of natural “Schumann” frequencies, facilitating the capture of useful electrical

power. Tesla also knew that the earth could be treated as one big spherical conductor and the ionosphere as another bigger spherical conductor, so that together they have parallel plates and thus, comprise a “spherical capacitor.” Dr. Rauscher calculates the capacitance to be about 15,000 microfarads for the complete earth-ionosphere cavity capacitor. W.O. Schumann is credited for predicting the “self-oscillations” of the conducting sphere of the earth, surrounded by an air layer and an ionosphere in 1952, without knowing that Tesla had found the earth’s fundamental frequency fifty years earlier.In comparison to the 3 billion kW available from the earth system, it is possible to calculate what the U.S. consumed in electricity. In 2000, about 11 Quads (quadrillion Btu) were actually used by consumers for electrical needs, which is equal to 3.2 trillion kWh. Dividing by the 8760 hours in a year, we find that only 360 million kW are needed on site to power our entire country. This would still leave 2.6 billion kW for the rest of the world! The reallyshameful U.S. scandal, unknown to the general public, is that out of the total electrical power generated using wire transmission (about 31 Quads), a full 2/3 is totally wasted in “conversion losses.” (Ref. Electricity Flow Chart 1999, which contains US DOE/EIA data, updating the Toby Grotz article in this book.) No other energy production system of any kind in the world has so much wastefulness. Instead of trying to build 2 power plants per week (at 300 MW each) for the next 20 years (only to have a total of additional 6 trillion kWh available by 2020), as some U.S. government officials want to do, we simply need to eliminate the 7 trillion kWh of conversion losses in our present electricity generation modality. Tesla’s wireless transmission of power

accomplishes this goal, better than any distributed generation.

Fig-1(losses in the wired system)2.2-Some advantages of WPT

At places where economic competition is not the prime consideration, it can be an option. Wireless power transmission can supply power to places that are difficult to reach. Especially small communities in rural areas could be supplied with power using WPT.

First of all the wireless electrical transmission of data removes the need for physical infrastructure like grids and towers. In this way the cost associated with deploying towers and cables can be saved.

During the rains and after natural disasters it is often hard to manage the cables and towers .by using WPT technology this problem can be eliminated.

The transmission and distribution loss associated with traditional electricity grids can be overcome.

Today two words are ruling the world “efficiency” and “speed”. These two words have become the base for the development in the technology.

The electricity generation using microwaves is more environments friendly. Moreover it does not involve any emission of carbon gases.

The ultimate benefit of this technology is transmission veracity and integrity. Many countries can enjoy the economic benefits of this technology. A signal resonant energy receiver is an ultimate device to connect various electrical applications.

The monthly electricity bills using conventional electricity supply can be cut to very low.

Use of battery for charging electrical and electronics devices can totally be eliminated.

3. HISTORY OF WPT

1820: André-Marie Ampère develops Ampere’s law showing that electric current produces a magnetic field.

1831: Michael Faraday develops Faraday’s law of induction describing the electromagnetic force induced in a conductor by a time-varying magnetic flux.

1864: James Clerk Maxwell synthesizes the previous observations, experiments and equations of electricity, magnetism and optics into a consistent theory and mathematically models the behavior of electromagnetic radiation.

1888: Heinrich Rudolf Hertz confirms the existence of electromagnetic radiation. Hertz’s "apparatus for generating electromagnetic waves" was a VHF or UHF "radio wave" spark gap transmitter.

1891: Nikola Tesla improves Hertz-wave wireless transmitter RF power supply or exciter in his patent No. 454,622, "System of Electric Lighting."

1893: Tesla demonstrates the wireless illumination of phosphorescent lamps of his design at the World's Columbian Exposition in Chicago.

Fig-2 (wardencliffe tower)

1894: Hutin & LeBlanc, espouse long held view that inductive energy transfer should be possible, they received U.S. Patent # 527,857 describing a system for power transfer at 3 kHz.

1894: Tesla wirelessly lights up single-terminal incandescent lamps at the 35 South Fifth Avenue laboratory, and later at the 46 E. Houston Street laboratory in New York City by means of "electrodynamic induction," that is to say wireless resonant inductive coupling.

1894: Jagdish Chandra Bose ignites gunpowder and rings a bell at a distance using electromagnetic waves, showing that communications signals can be sent without using wires.

1895: Bose transmits signals over a distance of nearly a mile.

1896: Tesla transmits signals over a distance of about 48 kilometres (30 mi).

1897: Guglielmo Marconi uses a radio transmitter to transmit Morse code signals over a distance of about 6 km.

1897: Tesla files the first of his patent applications dealing specifically with wireless transmission.

1899: In Colorado Springs, Tesla writes, "the inferiority of the induction method would appear immense as compared with the disturbed charge of ground and air method."

1900: Marconi fails to get a patent for radio in the United States.

1901: Marconi transmits signals across the Atlantic Ocean using Tesla's apparatus.

1902: Tesla vs. Reginald Fessenden - U.S. Patent Interference No. 21,701, System of Signaling (wireless); selective illumination of incandescent lamps, time and frequency domain spread spectrum telecommunications, electronic logic gates in general.

1904: At the St. Louis World's Fair, a prize is offered for a successful attempt to drive a 0.1 horsepower (75 W) airship motor by energy transmitted through space at a distance of least 100 feet (30 m).

1917: Tesla's Wardenclyffe tower is demolished. 1926: Shintaro Uda and Hidetsugu Yagi publish their first

paper on Uda's "tuned high-gain directional array"better known as the Yagi antenna.

1961: William C. Brown publishes an article exploring possibilities of microwave power transmission.

1964: Brown demonstrates on CBS News with Walter Cronkite a model helicopter that received all the power needed for flight from a microwave beam. Between 1969 and 1975, Brown was technical director of a JPL Raytheon program that beamed 30 kW over a distance of 1 mile at 84% efficiency.

1968: Peter Glaser proposes wirelessly transferring solar energy captured in space using "Powerbeaming" technology This is usually recognized as the first description of a solar power satellite.

1971: Prof. Don Otto develops a small trolley powered by induction at The University of Auckland, in New Zealan.

1973: World first passive RFID system demonstrated at Los-Alamos National Lab.

1975: Goldstone Deep Space Communications Complex does experiments in the tens of kilowatts.

1988: A power electronics group led by Prof. John Boys at The University of Auckland in New Zealand, develops an inverter using novel engineering materials and power electronics and

conclude that power transmission by means of electrodynamic induction should be achievable. A first prototype for a contact-less power supply is built. Auckland Uniservices, the commercial company of The University of Auckland, patents the technology.

1989: Daifuku, a Japanese company, engages Auckland Uniservices Ltd. to develop the technology for car assembly plants and materials handling providing challenging technical requirements including multiplicity of vehicles.

1990: Prof. John Boys team develops novel technology enabling multiple vehicles to run on the same inductive power loop and provide independent control of each vehicle. Auckland UniServices Patents the technology.

1996: Auckland Uniservices develops an Electric Bus power system using Electrodynamic Induction to charge (30-60 kW) opportunistically commencing implementation in New Zealand. Prof John Boys Team commission 1st commercial IPT Bus in the world at Whakarewarewa, in New Zealand.

1998: RFID tags powered by electrodynamic induction over a few feet

2001: Splashpower formed in the UK. Uses coupled resonant coils in a flat "pad" style to transfer tens of watts into a variety of consumer devices, including lamp, phone, PDA, iPod etc.

2004: Electrodynamic Induction used by 90 percent of the US$1 billion clean room industry for materials handling equipment in semiconductor, LCD and plasma screen manufacture.

2005: Prof Boys' team at The University of Auckland, refines 3-phase IPT Highway and pick-up systems allowing transfer of power to moving vehicles in the lab.

2007: Using Electrodynamic Induction a physics research group, led by Prof. Marin Soljačić, at MIT, wirelessly power a 60W light bulb with 40% efficiency at a 2 metres (6.6 ft) distance with two 60 cm-diameter coils.

2008: Bombardier offers new wireless transmission product PRIMOVE, a power system for use on trams and light-rail vehicles.

2008: Industrial designer Thanh Tran, at Brunel University made a wireless lamp incorporating a high efficiency 3W LED.

2008: Intel reproduces Nikola Tesla's original 1894 implementation of Electrodynamic Induction and Prof. John Boys group's 1988 follow-up experiments by wirelessly powering a nearby light bulb with 75% efficiency.

2008: Greg Leyh and Mike Kennan of the Nevada Lightning Laboratory publish a paper on Nikola Tesla's disturbed charge of ground and air method of wireless power transmission with

circuit simulations and test results showing an efficiency greater than can be obtained using the Electrodynamic Induction method.

2009: A Consortium of interested companies called the Wireless Power Consortium announced they are nearing completion for a new industry standard for low-power Inductive charging.

2009: An Ex approved Torch and Charger aimed at the offshore market is introduced.This product is developed by Wireless Power & Communication, a Norway based company.

2009: A simple analytical electrical model of resonance power transfer system is proposed and applied to wireless power transfer for implantable devices.

2009: Lasermotive uses diode laser to win $900k NASA prize in power beaming, breaking several world records in power and distance, by transmitting over a kilowatt more than several hundred meters.

2009: Sony shows a wireless electrodynamic-induction powered TV set, 60 W over 50 cm.

2010: Haier Group debuts “the world's first” completely wireless LCD television at CES 2010 based on Prof. Marin Soljačić's follow-up research on Nikola Tesla's electrodynamic induction wireless energy transmission method and the Wireless Home Digital Interface (WHDI).

4. THEORIES ON WPT

4.1-Near field theory

Near field is wireless transmission techniques over distances comparable to, or a few times the diameter of the device(s), and up to around a quarter of the wavelengths used. Near field energy itself is non radiative, but some radiative losses will occur. In addition there are usually resistive losses. Near field transfer is usually magnetic (inductive), but electric (capacitive) energy transfer can also occur.

4.1.1-Electrical conduction principle

Electrical energy can be transmitted by means of electrical currents made to flow through naturally existing conductors, specifically the earth, lakes and oceans, and through the upper atmosphere starting at approximately 35,000 feet (11,000 m) elevation — a natural medium that can be made conducting if the breakdown voltage is exceeded and the constituent gas becomes ionized. For example,

when a high voltage is applied across a neon tube the gas becomes ionized and a current passes between the two internal electrodes. In a wireless energy transmission system using this principle, a high-power ultraviolet beam might be used to form vertical ionized channels in the air directly above the transmitter-receiver stations. The same concept is used in virtual lightning rods, the electrolaser electroshock weapon and has been proposed for disabling vehicles. A global system for "the transmission of electrical energy without wires" dependant upon the high electrical conductivity of the earth was proposed by Nikola Tesla as early as 1904.

"The earth is 4,000 miles radius. Around this conducting earth is an atmosphere. The earth is a conductor; the atmosphere above is a conductor, only there is a little stratum between the conducting atmosphere and the conducting earth which is insulating. . . . Now, you realize right away that if you set up differences of potential at one point, say, you will create in the media corresponding fluctuations of potential. But, since the distance from the earth's surface to the conducting atmosphere is minute, as compared with the distance of the receiver at 4,000 miles, say, you can readily see that the energy cannot travel along this curve and get there, but will be immediately transformed into conduction currents, and these currents will travel like currents over a wire with a return. The energy will be recovered in the circuit, not by a beam that passes along this curve and is reflected and absorbed, . . . but it will travel by conduction and will be recovered in this way."

Researchers experimenting with Tesla's wireless energy transmission system design have made observations that may be inconsistent with a basic tenet of physics related to the scalar derivatives of the electromagnetic potentials, which are presently considered to be nonphysical. The intention of the Tesla world wireless energy transmission system is to combine electrical power transmission along with broadcasting and point-to-point wireless telecommunications, and allow for the elimination of many existing high-tension power transmission lines, facilitating the interconnection of electrical generation plants on a global scale. One of Tesla's patents suggests he may have misinterpreted 25–70 km nodal structures associated with cloud-ground lightning observations made during the 1899 Colorado Springs experiments in terms of circum globally propagating standing waves instead of a local interference phenomenon of direct and reflected waves. Regarding the recent notion of power transmission through the earth-ionosphere cavity, a consideration of the earth-ionosphere or concentric spherical shell waveguide propagation parameters as they are known today shows that wireless energy transfer by direct

excitation of a Schumann cavity resonance mode is not realizable. "The conceptual difficulty with this model is that, at the very low frequencies that Tesla said that he employed (1-50 kHz), earth-ionosphere waveguide excitation, now well understood, would seem to be impossible with the either the Colorado Springs or the Long Island apparatus (at least with the apparatus that is visible in the photographs of these facilities)."

Fig-3 (Tesla coil transformer wound in the form of a flat spiral. This is the transmitter form as described in U.S. Patent 645,576)

On the other hand, Tesla's concept of a global wireless electrical power transmission grid and telecommunications network based upon energy transmission by means of a spherical conductor transmission line with an upper three-space model return circuit, while apparently not practical for power transmission, is feasible, defying no law of physics. Global wireless energy transmission by means of a spherical conductor “single-wire” surface wave transmission line and a propagating TM00 mode may also be possible, a feasibility study using a sufficiently powerful and properly tuned Tesla coil earth-resonance transmitter being called for.

induction principle(non resonant energy transfer)

The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are not directly connected. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The Battery chargers of a mobile phone or the transformers on the street is examples of how this principle can be used. Induction cookers and many electric toothbrushes are also powered by this technique. The main drawback to induction, however, is the short range. The receiver must be very close to the transmitter or induction unit in order to inductively couple with it.

4.1.2- Electrostatic induction principle

Fig-4(Tesla illuminating two exhausted tubes by means of a powerful, rapidly alternating electrostatic field created between two vertical metal sheets suspended from the ceiling on insulating cords.)

The "electrostatic induction effect" or "capacitive coupling" is an electric field gradient or differential capacitance between two elevated electrodes over a conducting ground plane for wireless energy transmission involving high frequency alternating current potential differences transmitted between two plates or nodes. The electrostatic forces through natural media across a conductor situated in the changing magnetic flux can transfer energy to a receiving device (such as Tesla's wireless bulbs).Sometimes called "the Tesla effect" it is the application of a type of electrical displacement, i.e., the passage of electrical energy through space

and matter, other than and in addition to the development of a potential across a conductor.

Tesla stated,

"Instead of depending on [electrodynamic] induction at a distance to light the tube . . . [the] ideal way of lighting a hall or room would . . . be to produce such a condition in it that an illuminating device could be moved and put anywhere, and that it is lighted, no matter where it is put and without being electrically connected to anything. I have been able to produce such a condition by creating in the room a powerful, rapidly alternating electrostatic field. For this purpose I suspend a sheet of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal being preferably connected to the ground. Or else I suspend two sheets . . . each sheet being connected with one of the terminals of the coil, and their size being carefully determined. An exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere, even a certain distance beyond them; it remains always luminous.” and

“In some cases when small amounts of energy are required the high elevation of the terminals, and more particularly of the receiving-terminal D' may not be necessary, since, especially when the frequency of the currents is very high, a sufficient amount of energy may be collected at that terminal by electrostatic induction from the upper air strata, which are rendered conducting by the active terminal of the transmitter or through which the currents from the same are conveyed."

4.1.3- Electro-dynamic induction ( Resonant inductive coupling method/Evanescent coupling method)An inductive transformer is a device commonly used in power circuits and electromechanical motors (for example electrical toothbrushes and chargers). A transformer typically operates up to mid-kHz frequencies. It essentially transfers electrical energy from one circuit to another via induction: the time-varying magnetic flux produced by a primary coil crosses a secondary coil and induces in it a voltage. The primary and the secondary coils are not physically connected, hence the method is wireless. Transformers can be very efficient but the distance between the coils must be very small (typically a few millimetres). For distances a few times the size of the coils, the efficiency drops significantly. Part of the underlying physics for most of the existing methods for the wireless transfer of electricity is the fundamental principle of resonance: the property of certain physical systems to oscillate with maximum amplitudes at

certain frequencies. It follows that, for any type of excitation (mechanical, acoustic, electro magnetic, nuclear) with a given frequency, a receiver will pick up the transmitted energy efficiently only when designed to resonate at the excitation frequency. Only then do successive excitations after each oscillation period add coherently in phase and lead to a build up of energy within the receiver. To illustrate, consider 100 glasses filled with wine at different levels so that they support acoustic resonances at different frequencies. Now let an electric-guitar player produce and sustain a very well-defined note. Only one of the glasses, the one resonant with the frequency of this note, will respond to the excitation, to the extent that it may even break, while the rest will remain unaffected. Similarly, we tune the electromagnetic antenna of a radio to be resonant with the frequency of the station we want to listen to. Many transformers used in power circuitry and elsewhere are also designed to employ resonance to enhance the power transmission.

4.1.4-Experimental demonstration of evanescent coupling at MITRadiative modes of omni-directional antennas (which work very well for information transfer) are not suitable for such energy transfer, because a vast majority of energy is wasted into free space. Transmitting electricity within a room, namely over distances a few

times greater than the size of the receiving devices themselves (what engineers define as mid-range distances), is a challenge for most modern applications. Achieving this goal with satisfactory efficiency, safety and low cost remains an unsolved problem. That was the challenge for Soljac`´ic´ and his collaborators at the MIT labs: John Joannopoulos, Peter Fisher, Andre Kurs, Robert Moffatt . The energy of any resonator naturally decays due to intrinsic energy-loss mechanisms (friction for mechanical resonances, radiation and resistive absorption for electromagnetic resonances, collisions with phonons and spontaneous emission for atomic resonances). Losses are typically quantified by the number of oscillation periods that it takes for the energy to decay by a factor of 2.72. This number, represented by the “quality factor” Q, is an intrinsic property of resonators and depends on the strength of the loss mechanisms. (As a simple analogue, water inside a bucket with a hole will leak out at a rate that depends on the size of the hole.) If two equal resonators exchange energy, it also takes a characteristic number of oscillation periods to transfer the energy from resonator A to resonator B, which is proportional to a constant that quantifies the strength of the coupling between the resonators, Qk. (If water is pumped from one bucket to another via a hose, then the transfer time depends on the strength of the pump.) Clearly, for energy

transfer to be efficient, Qneeds to be much larger than Qk, i.e. the rate at which energy is being transferred needs to far exceed the rate at which energy is being lost. (Water will be efficiently transferred between two leaking buckets if the pump is faster then the leaks from the holes.) The efficiency of the system can then be characterized by Q/Qk. Thetransfer of energy is efficient only when this ratio is larger than one, the so-called strong-coupling regime. For our wireless method, they used one of the most basic electric circuits as a resonator: the LC circuit. This circuit is an electromagnetic resonant circuit that consists of an inductor (L), made by a wire coil, and a capacitor (C). Two such wire coils transfer energy via induction, like a transformer device, and the Qk clearly depends on the distance between the coils. For mid-range distances and long enough wavelengths, the spatial-decay rate of the magnetic field means that Qk is roughly proportional to the cube of the ratio of the distance between the coils, D, and the size of each coil, d, while showing little dependency on the frequency and the geometry of the coils. This means that, for mid-range distances, Qk will be large and the coupling very weak. As a result, the best way to maximize the efficiency is to engineer the resonators to have the highest possible value of Q(try to seal the holes in the buckets). The resonance frequency of each coil (which has to be the same for both coils) can be tuned by varying the capacitance (and tuning a circuit element is exactly what the knob is tuning in a radio antenna). Qvaries with the tuneable frequency, and this variation is shown in the figure above for a coil with a diameter of 60 cm made of copper pipe with a radius of 2 cm. It can be seen that, for high-MHz frequencies, the resonator loses energy fast (low Q, often even less than 10) due to radiation. This is exactly how an antenna is designed to work. Similarly, for mid-kHz frequencies, it loses energy fast (Q less than 100) via resistive absorption, which is typical of transformers. This explains why both omni-directional antennas and transformers fail to be efficient power transmitters at mid-range distances: the transfer-time measure Qk is large because of D, and Q is small. On the other hand, in the intermediate, low-MHz regime, much longer loss-times are observed, with Q often larger than 1000. That was their chosen

regime.

Fig-5 ( ligtening a 60 watt bulb around 2m away from the source at MIT)Based on their theory, they started experiments in late 2006. The main challenges consisted of designing a driving circuit that would operate in our desired low-MHz regime and constructing coils that would resonate with a high enough value of Q. After a trial-and-error phase, they realized that a simple coil design without a separate capacitor, but using the coil’s self-capacitance to achieve resonance, was the best option in terms of Q. We made two copper-pipe coils with 60 cm diameters and with five turns, such that they resonate at 10MHz and have Q=1000. A 60 W light bulb was the chosen device, since it operates at the tested frequencies (and what can be a clearer sign of the functionality of a system than the switch on of a light bulb?). They suspended the coils from the ceiling with fishing wire, at a distance of 2m from each other, tuned them up, turned them on and…there was light. At an efficiency of 45%, this was, to our knowledge, the first-ever demonstration of midrange efficient wireless energy transfer.4.2- Far field theoryFar field methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). With radio wave and optical devices the main reason for longer ranges is the fact that electromagnetic radiation in the far-field can be made to match the shape of the receiving area (using high directivity antennas or well-collimated Laser Beam) thereby delivering almost all emitted power at long ranges. The maximum directivity for antennas is physically limited by diffraction.The Raytheon Company did the first successful WPT experiment in 1963. In this experiment energy was transmitted with a DC-to-DC

efficiency of 13%. This company also demonstrated a microwave-powered helicopter in 1964 [2]. The Jet propulsion lab of NASA carried out an experiment and demonstrated the transfer of 30 kW over a distance of 1 mile in 1975. They used an antenna array erected at the Goldstone facility. This test demonstrated the possibilities of wireless power outside the laboratory. Rockwell International and David Sarnoff Laboratory operated in 1991 a microwave powered rover at 5.86 GHz. Three kilowatts of power was transmitted and 500 watts was received .

4.2.1 – Microwave Power Transmission(MPT)In order to transport electricity is has to be transformed into a suitable energy form. For wireless transmission, this has to be a form that can travel trough air. Microwave frequencies hold this ability. The microwave spectrum is defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. A complete microwave transmission system consists of three essential parts:

Electrical power to microwave power conversion Absorption antenna that captures the waves (Re)conversion to electrical power

Fig-6(Microwave transmitter and rectenna)

The components include a microwave source, a transmitting antenna and a receiving antenna. The microwave source consists of an electron tubes or solid-state devices with electronics to control power output. The slotted waveguide antenna, parabolic dish and microstrip patch are the most popular types. Due to high efficiency (>95%) and high power handling capacity, the slotted waveguide antenna seems to be the best option forpower transmission. The combination of receiving and converting unit is called rectenna. The rectenna is a rectifying antenna that is used to directly convert microwave

energy into DC electricity. It is an antenna includes a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional. One of the disadvantages is that microwaves have long wavelengths that exhibit a moderate amount of diffraction over long distances. The Rayleigh criterion dictates that any beam will spread (microwave or laser), become weaker, and diffuse over distance. The larger the transmitter antenna orlaser aperture, the tighter the beam and the less it will spread as a function of distance (and vice versa). Therefore, the system requires large transmitters and receivers. The used power density of the microwave beam is normally in de order of 100 W/m2. This is relative low compared to the power density of solar radiation on earth (1000 W/m2) and chosen this way for safety reasons. 4.2.2-Applications

WTP for space solarThe largest application for microwave power transmission is space solar power satellites (SPS). In this application, solar power is captured in space and converted into electricity. The electricity is converted into microwaves and transmitted to the earth. The microwave power will be captured with antennas and converted into electricity. NASA is still investigating the possibilities of SPS. One of the problems is the high investment cost due to the space transport. The current rates on the Space Shuttle run between $7,000 and $11,000 per kilogram of transported material. Recently the idea of Space Solar Power caught again the public attention e.g. by the Obama transition team and The Economist .

Fig-7 ( Space Solar Power satellite)

Power transfer, bridging applicationsUsing a powerful focused beam in the microwave or laser range long distances can be covered. There are two methods of wireless power transmission for bridging application. First is the direct method, from transmitting array to rectenna. A line of sight is needed and is therefore limited to short (< 40 km) distances. Above 40 kilometers, huge structures are needed to compensate for the curvature of the earth. The second method is via a relay reflector between the transmitter and rectenna. This reflector needs to be at an altitude that is visible for both transmitter and rectenna. Next one bridging applications of WPT are discussed.

Alaska '21WPT can be an option for power supply to rural areas. In 1993 was a project presented about wireless power supply in Alaska. Because of limited infrastructure, hundreds of small rural communities in Alaska must provide their own electricity. These systems can be expensive not standard or just not available. At the moment, the small communitiesproduce their own power with mainly diesel engines. These produce noise and pollution. Also the needed fuel has to be transported over long distances. All this results in an electricity price in excess of $40/kWh [14].Cable connections trough water is no option because of ice. With the help of WPT, the needed power production of the communities can be combined. This can reduce noise, pollution and transportation of fuel.WPT may be capable of transmitting electrical energy to Alaska’s remote villages. To investigate these possibilities, a pilot project was conducted named "Alaska'21”. The system used for the pilot project consisted of a2.45 GHz phased array design. The distances that should be bridged are between 1 and 15 miles. The status of the project is unknown.

FIG-8(Alaska’21 )

4.2.3- Safety issues Bio-effects

A general public perception that microwaves are harmful has been a major obstacle for the acceptance of power transmission with microwaves. A major concern is that the long-term exposure to low levels of microwaves might be unsafe and even could cause cancer. Since 1950, there have been thousands of papers published about microwave bio-effects. The scientific research indicates that heating of humans exposed to the radiation is the only known effect. There are also many claims of low-level non thermal effects, but most of these are difficult to replicate or show unsatisfying uncertainties. Large robust effects only occur well above exposure limits existing anywhere in the world . The corresponding exposure limits listed in IEEE standards at 2.45 or 5.8 GHz are 81.6 W/m2 and 100 W/m2 averaged over 6 minutes, and 16.3 or 38.7 W/m2 averaged over 30 minutes . This low compared to average solar radiation of 1000 W/m2. A clearly relevant bio-effect is the effect of microwave radiation on birds, the so-called "fried bird effect". Research is done on such effect at 2.45 GHz. The outcome showed slight thermal effects that probably are welcome in the winter and to be avoided in the summer . Larger birds tend to experience more heat stress then small birds . The overall conclusion of bioeffects research is that microwave exposures are generally harmless except for the case of penetrating exposure to intense fields far above existing exposure

limits .

Fig-9(graph showing safety level to different range of fre.)Further discussions about the maximum microwave power density are necessary. A range of issues and safety-related factors should continue to receive consideration because of public concern about radio wave and micro wave exposure.

Compatibility with other radio services and applicationsIt is assumed that WPT systems working with microwaves use frequency bands around 2.45 GHz or 5.8 GHz. These bands are already allocated in the ITU-R radio regulation to a number of radio services. They are also designated for industrial science and medical (ISM applications). The ISM band is, as presently defined, for local use only. The 2.45 GHz is further more used for radio LAN and microwave ovens. The 5.8 GHz is also used heavily for various applications like Radiolocation service and DSRC (Dedicated Short-Range Communications). More investigation is needed to get an image of the possible influencing between the systems .

5. How WPT technology worksA copper coil attached to a power source is the sending unit. Another coil, attached to the device to be induced is the receiver which makes it possible for energy to be transferred from one to the other. There are particular advantage on effective distance, maximum power transfer, control level and efficiency for each approach. We designed to make use of an advantageous position respectively and started to construct a simple, safe and efficient

Wireless Charging Pad.

Fig-10(block diagram showing transmitter module and receiver module)Our design are the combination of both technologies which not only transfer power through wireless by electromagnetic induction, but also contain self-resonance at the side of transmitter and receiver independently in order to achieve better efficiency and hence reduce the power loss.

Block description“One Plug, One Pad, Various devices”; whole system only consists of a transmitter and a receiver. The transmitter is a platform where powers by a one plug that is transmitted to the devices. It can simultaneously power wide variety of devices which their receiver module is placed around the protuberance of the pad’s surface. The devices are electrically charged as if they are plugged into a conventional adapter, irrespective of their position or orientation. The receiver, differently, is integrated into electronic devices such as mobile phones or PDA and allows an electronic device to receive charge from the transmitter. Consequently, electrical current creates magnetic fields and vice versa. This technology takes advantage of the fact that magnetic fields can travel through free space. Electrical current in the base station creates a magnetic field that wirelessly carries the power to the receiver where it is converted back to electrical current. This coupling provides a secure charging condition because it is electrically isolated between powered transmitter and users.

6. OVERVIEW OF FUTURE WITH WIRELESS TRANSMISSION OF ELECTRICITYAs Tesla himself said,

“In the near future we shall see a great many uses of electricity…we shall be able to disperse fogs by electric force and powerful and penetrative rays…wireless plants will be installed for the purpose of illuminating the oceans…picture transmission by ordinary telegraphic methods will soon be achieved…another valuable novelty will be a typewriter electrically operated by the human voice…we shall have smoke annihilators, dust absorbers, sterilizers of water, air, food and clothing…it will become next to impossible to contract disease germs and country folk will go to town to rest and get well…”

In the macroscopic world, this scheme could potentially be used to deliver power to robots and/or computers in a factory room, or electric buses on a highway (source-cavity would in this case be a “pipe” running above the highway).

In the microscopic world, where much smaller wavelengths would be used and smaller powers are needed, one could use it to implement optical inter-connects for CMOS electronics, or to transfer energy to autonomous nano-objects (e.g. MEMS or nano-robots) without worrying much about the relative alignment between the sources and the devices.

7. CONCLUSION

This technology is a big impediment to development in the retail sector right now.

The wireless transfer of electricity has been a sci-fi dream up to this point ,and truly, if electricity could simply be in the air, in the same way radio waves and wi-fi signals are, it would change the world.

8.REFERENCES

1) Tesla, N. “Apparatus for transmitting electrical energy.” U.S. patent number 1,119,732, issued in December 1914. 2) Fernandez, J. M. and Borras, J. A. “Contactless battery charger with wireless control link.” U.S. patent number 6,184,651, issued in February 2001. 3) Ka-Lai, L., Hay, J. W. and Beart, P. G. W. “Contact-less power transfer.” U.S. patent number 7,042,196, issued in May 2006. (SplashPower Ltd., www.splashpower.com) 4) Esser, A. and Skudelny, H.-C. “A new approach to power supplies for robots.” IEEE Trans. on industry applications 27, 872 (1991). 5) Hirai, J., Kim, T.-W. and Kawamura, A. “Wireless transmission of power and information and information for cableless linear motor drive.” IEEE Trans. on power electronics 15, 21 (2000).

6) Scheible, G., Smailus, B., Klaus, M., Garrels, K. and Heinemann, L. “System for wirelessly supplying a large number of actuators of a machine with electrical power.” U.S. patent number 6,597,076, issued in July 2003. (ABB, www.abb.com)

7) H. Feingold et al., Space Solar Power: A Fresh Look at the Feasibility of Generating Solar Power in Space for Use on Earth, April 4, 1997, SAIC Report 97/1005 for contract NAS3–26565.8) Space Solar Power: Advanced Concepts Study Project, Technical Interchange Meeting, Sept. 19–20 1995, NASA Headquarters, Washington DC.9) G. Landis, “A Supersynchronous Solar Power Satellite,” SPS-97: Space and Electric Power for Humanity, Aug. 24–28, 1997, Montreal, Canada, pp. 327–328.10) G. Landis, “An Evolutionary Path to SPS,” Space Power, Vol. 9 No. 4, pp. 365–371 (1990).11) G. Landis and R. Cull, “Application of Thin Film Technology Toward a Low-Mass Solar Power Satellite,” Vision-21 Symposium Proceedings, NASA CP–10059, April 1990, pp. 494–500.12) G. Landis and R. Cull, “Integrated Solar Power Satellites: An Approach to Low-Mass Space Power,”Space Power, Vol. 11, No. 3–4, 303–218 (1992); presented at SPS-91: Power From Space, Aug. 27–30, 1991, Paris France, pp. 225–23213) www.witricity.com